Various types of medicated patches containing medicinal agents are being developed with expectations of reducing side-effects caused by tissue absorption of the medicinal agents into the gastrointestinal tract and avoiding first pass into the liver, and of improving patient compliance.
However, not all medicinal agents exhibit satisfactory tissue absorption with transdermal administration, transmucosal administration or transnail administration, and much investigation has been conducted to improve tissue absorption.
Medicinal agents are available on the market in the form of acid addition salts, from the viewpoint of handleability and stability. However, it is generally known that when medicinal agents of acid addition salts are directly applied by transdermal administration, their tissue absorption tends to be lower. On the other hand, it is also known that free bases (free forms) of medicinal agents are preferred for tissue absorption.
Methods of neutralizing (desalting) acid addition salts of medicinal agents to be used in medicated patches, using metal hydroxides such as sodium hydroxide, as strong bases which completely desalt the acid addition salts, have been investigated (Patent documents 1 and 2, for example), but all of these methods either eliminate beforehand the metal salts produced by filtration treatment, or mix them with adhesive base materials.    [Patent document 1] Japanese Unexamined Patent Application Publication No. 2007-16020    [Patent document 2] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-509874